An investigation of rainfall variability in the upper and lower river Niger basin development authority areas, Nigeria

The paper investigates annual rainfall variability in the Upper and Lower Niger Basin Development Authority Areas. The annual rainfall series is investigated for variability using Standardized Anomaly Index and Gaussian Lower pass filter. It is also examined for trends using Spearman’s rank correlation coefficient. The annual rainfall over the study area exhibits multi-decadal drying trend from 1970-1993, as well as strong inter-annual variability.  The annual rainfall series shows an insignificant trend during the 1941-2010 period but increasing trend during the 1980-2010 sub period. Recovery of annual rainfall occurred at the end of the long persistent dry period.